Electronic devices typically comprise one or more electrical circuits encapsulated in a polymer such as epoxy. Electrically conductive leads from the circuits extend through the encapsulant for connection to other electronic devices. One particular lead arrangement is the so-called "gull wing" arrangement wherein the leads extend from the midpoint of the height of the encapsulated package, downwardly to a point slightly below the lower surface of the package and outwardly parallel to this surface.
To test such devices it is typical to place the device in a test socket attached to a test apparatus including a printed circuit board and electrically operate the device, sometimes in an elevated temperature environment. The test socket must be designed to easily allow rapid insertion and withdrawal of the device without damaging the device leads. Most desirable types of sockets include a zero-insertion-force (ZIF) or zero-insertion-pressure (ZIP) arrangement wherein the device can be inserted into or withdrawn from the socket without placing any stress on the package leads. These types of sockets are distinct from sockets which utilize frictional interference between the leads and the socket contacts to provide the necessary electrical contact between the device and the socket.
One of a large number of ZIF sockets is described in U.S. Pat. No. 5,195,903 wherein a series of contacts are operated by a lever to move toward and away from a device inserted into a well in the center of the socket. The contacts move in a arc up and away from the leads of the device as the socket lever is actuated. A spring portion of the contact is provided to accommodate this motion and provide the spring force necessary to make adequate electrical contact with the leads of the device. The problem with this arrangement is that the spring portion of the contact must perform two functions and thus is something of a compromise. If the spring constant of the contact is set high in order to increase the contact force on the device leads, as by increasing the section of the spring portion of the contact, the necessary operating force is also increased. On the other hand, if the spring constant of the contact is set low, in order to reduce necessary operating force, the contact force is also reduced. Thus existing ZIF sockets for gull wing devices have the inherent disadvantage in that it is difficult to provide a design which allows both the necessary operating force to be reduced as much as possible and the contact force to be increased.